Polyolefin type resinous composition

ABSTRACT

A polyolefin type resinous composition comprising 99 to 80% by weight of a propylene type block copolymer [A] and 1 to 20% by weight of an ethylene type or styrene type elastomer [B] which being superior in a transparency, a coloring property and a dimensional stability is provided. 
     The said polyolefin composition comprises the said [A] consisting of a propylene homopolymer component and an ethylene propylene copolymer component having respective limiting viscosities: [η] PP , [η] RC , weight %: W PP , W RC , and melt flow rates: [MFR] PP , [MFR] RC , as well as the said [B] having a limiting viscosity: [η] R  and a melt flow rate: [MFR] R , in such a way that the following relationships being established; 
     
       
         ([η] RC /[η] PP )×( W   PP   /W   RC )=0.2-3.0, 
       
     
     
       
         ([ MFR]   RC   /[MFR]   PP )=0.3-4.0, 
       
     
     
       
         [η] RC /[η] PP =0.7-1.2, 
       
     
     
       
         [η] RC &gt;6.5, 
       
     
     
       
         [ MFR]   R   /[MFR]   PP =0.3-4, 
       
     
     and 
     
       
         [η] R /[η] PP =0.7-1.2.

TECHNICAL FIELD

This invention relates to a polyolefin type resinous composition whichis superior in a transparency, a coloring property when pigment(s) beingadded and a dimensional stability.

BACKGROUND ART

Moldings made with use of polypropylenes (propylene homopolymer,ethylene-propylene copolymer, ethylene-propylene block copolymer) arerelatively superior in an economical efficiency and have been used forwide fields. However, moldings made with use of propylene homopolymerhave a high rigidity but have a disadvantage of a poor impactresistance, particularly a poor impact resistance at a low temperature.Thus, there have been hitherto made many propositions in order toimprove an impact resistance at a low temperature.

In those propositions, propylene type block copolymers have beenprepared generally by forming at first homopolymer components and thenintroducing ethylene-propylene random copolymer components. Sincemoldings made with use of propylene type block copolymers are superiorin an impact resistance at a low temperature, they are used widely invarious industrial fields such as automobiles and household electricappliances.

However, moldings made with use of conventional propylene type blockcopolymers are superior in an impact resistance but they have notransparency, thus they have such a disadvantage that they are notcolored well when various pigments being added and they have such anadditional disadvantage that a dimensional stability is bad.

DISCLOSURE OF THE INVENTION

We inventors made extensive researches with an object to solve theabove-mentioned problems, to attain a polyolefin type resinouscomposition which is superior in a transparency, a coloring propertywhen pigment(s) being added and a dimensional stability by controlling aproduct of a polymerization forming ratio of a homopolymer component toa copolymer component and a respective limiting viscosity ratio within aspecified range, furthermore controlling a ratio of a melt flow rate ofa homopolymer component to a melt flow rate of an ethylene-propylenecopolymer component, and furthermore controlling a ratio of a melt flowrate of the homopolymer component in the propylene type block copolymercomposition [A] to a melt flow rate of the olefin type or styrene typeelastomer ([MFR]_(R)/[MFR]_(PP)) as well as a ratio of a limitingviscosity of the homopolymer component in the propylene type blockcopolymer composition [A] to a limiting viscosity of the olefin type orstyrene type elastomer ([η]_(R)/[η]_(PP)) in a propylene type blockcopolymer composition [A] obtained by forming a homopolymer in gaseousphase polymerization and thereafter polymerizing an ethylene-propylenecopolymer component.

As clear from the above-mentioned explanation, the object of the presentinvention is to provide a polyolefin type resinous composition which issuperior in a transparency, a coloring property when pigment(s) beingadded and a dimensional stability.

The present invention has the following constructions.

(1) A polyolefin type resinous composition comprising 99˜80% by weightof a propylene type block copolymer [A] wherein the said block copolymerconsists of a propylene homopolymer component and an ethylene-propylenecopolymer component, a product of a limiting viscosity ratio of the saidcopolymer component to the said homopolymer component and a weight ratioof the said homopolymer component to the said copolymer component iswithin a range of

(([η]_(RC)/[η]_(PP))×(W _(PP) /W _(RC)))=0.2˜3.0,

wherein a limiting viscosity of the said homopolymer component being[η]_(PP), a limiting viscosity of the said copolymer component being[η]_(RC), a weight of the said homopolymer component being W_(PP) and aweight of the said copolymer component being W_(RC), as well as a ratioof a melt flow rate of the said homopolymer component to a melt flowrate of the said copolymer component is within a range of

([MFR] _(RC) /[MFR] _(PP))=0.3˜4.0,

a ratio of a limiting viscosity in the said homopolymer component to thesaid copolymer component is within a range of

[η]_(RC)/[η]_(PP)=0.7˜1.2,

and [η]_(RC) of the said copolymer component is 6.5 or less, and 1˜20%by weight of an ethylene type or styrene type elastomer [B] wherein aratio of a melt flow rate of the homopolymer component in the saidpropylene type block copolymer [A] to a melt flow rate of the lattermentioned olefin type or styrene type elastomer is within a range of

([MFR] _(R) /[MFR] _(PP))=0.3˜4,

and a ratio of a limiting viscosity [η]_(PP) in the homopolymercomponent in the said propylene type block copolymer [A] to a limitingviscosity of the latter mentioned olefin type or styrene type elastomer[η]_(R) is within a range of

[η]_(R)/[η]_(PP)=0.7˜1.2.

(2) A polyolefin type resinous composition according to theabove-mentioned (1) wherein the copolymer component in the propylenetype block copolymer (A) contains an ethylene weight unitof 25˜55% byweight based on the copolymer component weight.

(3) A polyolefin type resinous composition according to theabove-mentioned (1) wherein the propylene type block copolymer (A)contains a copolymer component of 22˜70% by weight based on the weight.

(4) A polyolefin type resinous composition according to theabove-mentioned (1) wherein the olefin type or styrene type elastomer[B] is ethylene-butene rubber.

(5) A polyolefin type resinous composition comprising 100 parts byweight of the polyolefin type resinous composition according to theabove-mentioned (1) to (4) and 0.001˜0.1 parts by weight of a molecularweight decreasing agent (C).

BEST MODE FOR CARRYING OUT THE INVENTION

The invention is illustrated as follows.

Necessary conditions of the propylene type block copolymer composition[A] used in the invention are that a relationship formula betweencontents and respective limiting viscosities in the homopolymercomponent and the copolymer component([η]_(RC)/[η]_(PP))×(W_(PP)/W_(RC)) is within a range of 0.2˜3.0, morepreferably 0.3˜2.7, that a ratio of a melt flow rate of the saidhomopolymer component to a melt flow rate of the said copolymercomponent. ([MFR]_(RC)/[MFR]_(PP)) is within a range of 0.3˜4, morepreferably 0.3˜3.5, that a limiting viscosity of the copolymer component[η]_(RC) is 6.5 or less, more preferably 5.0 or less, and that a ratioof a limiting viscosity ratio of the homopolymer component to a limitingviscosity of the copolymer component, [η]_(ER)/[η]_(PP), is within arange of 0.7˜1.2, preferably 0.8˜1.2.

Furthermore, the olefin type or styrene type elastomer has a ratio of amelt flow rate of the homopolymer component in the propylene type blockcopolymer composition [A] to a melt flow rate of the olefin type orstyrene type elastomer ([MFR]_(R)/[MFR]_(PP)) is within a range of0.3˜4, more preferably 0.3˜3.5, and a ratio of a limiting viscosityratio of the homopolymer component of the propylene type block copolymercomposition [A] to a limiting viscosity of the olefin type or styrenetype elastomer ([η]_(R)/[η]_(PP)) is within a range of 0.3˜4, morepreferably 0.3˜3.5, from a viewpoint of a transparency in the obtainedresinous composition.

A copolymer component content of the said propylene type block copolymercomposition [A] is preferably within a range of 22˜70% by weight, morepreferably 23˜55% by weight, from viewpoints of a transparency anddimensional a stability in the obtained resinous composition as well asfrom an economical viewpoint due to superior flowability in the formedpowders during preparation of the said propylene type block copolymercomposition [A].

An ethylene content in the said copolymer component is preferably withina range of 25˜55% by weight, more preferably 30˜55% by weight, from aviewpoint of a transparency in the obtained resinous composition.

As to the propylene type block copolymer composition [A] used in theinvention, a crystalline homopolymer component is prepared at first,which is determined directly about a limiting viscosity ([η]_(PP)) and amelt flow rate (MFR_(PP)). Describing as to a determination method of alimiting viscosity ([η]_(RC)) in the copolymer component, that is, thepropylene-ethylene random copolymer formed subsequently, at first alimiting viscosity [η]_(PP) of the obtained total propylene type blockcopolymer composition [A] is determined, then a product of a homopolymercomponent weight ratio and a limiting viscosity [η]_(PP) of thehomopolymer component is substracted from a limiting viscosity of thetotal composition ([η]_(WHOLE)), and the obtained value is divided by aratio of the total composition, i.e. the copolymer component, to give aquotient, which is a limiting viscosity [η]_(RC) of the copolymer part.That is, it is calculated by the following formula (1). $\begin{matrix}{\lbrack\eta\rbrack_{RC} = \frac{\lbrack\eta\rbrack_{WHOLE} - {( {1 - {W_{RC}/100}} )\quad\lbrack\eta\rbrack}_{PP}}{W_{RC}/100}} & {{formula}\quad (1)}\end{matrix}$

Furthermore, a melt flow rate of the above-mentioned copolymer component(MFR_(RC)) is obtained by determining a melt flow rate of the totalcopolymer composition (MFR_(WHOLE)) and a melt flow rate of thehomopolymer (MFR_(PP)) and then calculating by the following formula(2). $\begin{matrix}{{{Log}( {MFR}_{RC} )} = \frac{{{Log}( {MFR}_{WHOLE} )} - {( {1 - {W_{RC}/100}} ){{Log}( {MFR}_{PP} )}}}{W_{RC}/100}} & {{formula}\quad (2)}\end{matrix}$

The copolymer component ratio (W_(RC)/100) in the formulae can beobtained by means of conventional known methods such as an infraredanalytic method etc.

The propylene type block copolymer composition [A] used in the inventionmay be obtained by any method.

For example, blends obtained by adding and mixing homopolymers with EPRhaving a limiting viscosity ratio defined in the invention may be used.Furthermore, blends obtained by adding and mixing homopolymers andethylene-propylene random copolymers polymerized with use of atitanium-containing solid catalyst component may be used. However, amethod to polymerize a homopolymer component at first and thencontinuously prepare a copolymer component is most preferable from aneconomical viewpoint.

The olefin type or styrene type elastomers [B] used in the invention areelastomers showing a low crystallinity or an amorphousness, and they maybe exemplified by ethylene-propylene rubber, ethylene-butene rubber,propylene-butene rubber, styrene-ethylene-butadiene rubber,styrene-ethylene-propylene rubber and hydrogenated styrene-butadinerubber etc.

As to the olefin type or styrene type elastomer [B] used in theinvention, an ethylene content is preferably 40˜90% by weight, morepreferably 70˜80% by weight in the ethylene type elastomer, a propylenecontent is preferably 40˜90% by weight, more preferably 70˜80% by weightin the propylene type elastomer, and a styrene content is preferably40˜90% by weight, more preferably 70˜80% by weight in the styrene typeelastomer, from viewpoints of a rigidity, and MFRR is preferably 25 g/10min or less from a viewpoint of an impact resistance in the obtainedcomposition.

An amount of the said olefin or styrene type elastomer [B] added ispreferably 1˜20 parts by weight from viewpoints of a rigidity, an impactresistance and an appearance in the obtained composition.

As the molecular weight decreasing agent (C) used in the inventionaccording to the above-mentioned (5), organic peroxides are illustratedby example, and concretely the followings may be exemplified: benzoylperoxide, t-butyl perbenzoate, t-butyl peracetate, t-butylperoxyisopropyl carbonate, 2,5-di-methyl-2,5-di-(t-benzoylperoxy)hexane,2,5-di-methyl-2,5-di-(t-benzoylperoxy)hexyne-3, t-butyl-di-peradipate,t-butylperoxy-3,5,5-trimethyl hexanoate, methyl-ethyl ketone peroxide,cyclohexanone peroxide, di-t-butyl peroxide, dicumyl peroxide,2,5-di-methyl-2,5-di-(t-butylperoxy)hexane,2,5-di-methyl-2,5-di-(t-butylperoxy)hexyne-3,1,3-bis-(t-butylperoxyisopropyl)benzene, t-butyl cumyl peroxide,1,1-bis-(t-butylperoxy)-3,3,5-trimethyl cyclohexane,1,1-bis-(t-butylperoxy)cyclohexane, 2,2-bis-(t-butylperoxybutane,p-menthane hydroperoxide, di-isopropyl benzene hydroperoxide, cumenehydroperoxide, t-butyl hydroperoxide, p-cymene hydroperoxide,1,1,3,3-tetra-methyl butyl hydroperoxide and2,5-di-methyl-2,5-di-(hydroperoxy)hexane. An amount of the molecularweight decreasing agent added is 0.001˜0.1 parts by weight, preferably0.01˜0.05 parts by weight.

To the polyolefin type resinous compositions according to the invention,known additives used in the conventional polyolefins may be added ifnecessary. As the known additives, there may be exemplified anantioxidant, a dispersant, an ultraviolet absorber, a neutralizer, anantistatic agent, a pigment and a lublicant etc.

As preparation methods for the polyolefin type resinous compositionsaccording to the invention, there may be exemplified methods forpreparation by using the conventional known benders such as monoaxial orbiaxial extruders, bambary mixers, kneaders or rolls etc.

Various moldings may be obtained by using the polyolefin type resinouscomposition according to the invention by means of various moldingmethods such as an injection molding, an extruding molding, a vacuummolding and an air pressure forming etc. as occasion demands, but aninjection molding is preferable.

EMBODIMENTS

The following Examples and Comparative Examples illustrate the presentinvention more concretely, but the invention is not limited to them.

In the following Examples and Comparative Examples, the evaluationmethods described below were carried out.

Evaluation Methods

♦a melt flow rate

It was carried out according to a method defined in JIS K6758 at adetermination temperature of 230° C. under a load of 2.16 kg. (unit:g/10 min)

♦a coloring property

1 part by weight of a pearl pigment (made by Marl Corporation Co. Ltd.:mica pigment) was added to resinous compositions shown in Examplesaccording to the invention or Comparative Examples to obtain moldings,which were evaluated by observing with the naked eye.

◯: good pearl feeling

×: bad pearl feeling

♦a haze test (transparency)

It was determined according to a method defined in JIS K7105 at a testpiece thickness of 2 mm. (unit: %)

Transparency can be said good if a haze value (a cloudy value) beinglow.

♦a coefficient of linear expansion (dimensional stability)

It was carried out according to a method defined in JIS K7197 at atemperature raising rate of 5° C./min under a load of 2 g and at adetermination temperature of −30° C.˜80° C. (unit: ×10⁻⁵ cm/cm·° C.)

Dimensional stability can be said good if a coefficient of linearexpansion being low.

Blending Components

PP-1

Propylene type block copolymer having a melt flow rate (230° C., 2.16 kgload) of 6.0 g/10 min, an ethelene content in the copolymer component of35%, a copolymer component content of 28.7%,

(η_(RC)/η_(PP))×(W_(PP)/W_(RC)): 2.5,

MFR_(RC)/MFR_(PP): 1.1,

η_(RC)/η_(PP): 1.0, and

η_(RC): 1.8.

PP-2

Propylene type block copolymer having a melt flow rate (230° C., 2.16 kgload) of 2.5 g/10 min, an ethylene content in the copolymer component of48%, a copolymer component content of 36.7%,

(η_(RC)/η_(PP))×(W_(PP)/W_(RC) ): 1.8,

MFR_(RC)/MFR_(PP): 0.8,

η_(RC)/η_(PP): 1.1, and

η_(RC): 2.2.

PP-3

Propylene type block copolymer having a melt flow rate (230° C., 2.16 kgload) of 7.5 g/10 min, an ethylene content in the copolymer component of25%, a copolymer, component content of 50%,

(η_(RC)/η_(PP))×(W_(PP)/W_(RC)): 1.2,

MFR_(RC)/MFR_(PP): 2.0,

η_(RC)/η_(PP): 0.9, and

η_(RC): 1.5.

PP-4

Propylene type block copolymer having a melt flow rate (230° C., 2.16 kgload) of 8.7 g/10 min, an ethylene content in the copolymer component of26%, a copolymer component content of 40.7%,

(η_(RC)/η_(PP))×(W_(PP)/W_(RC)): 1.9,

MFR_(RC)/MFR_(PP): 0.6,

η_(RC)/η_(PP): 1.1, and

η_(RC): 1.6.

PP-5

Propylene type block copolymer having a melt flow rate (230° C., 2.16 kgload) of g/10 min, an ethylene content in the copolymer component of %,a copolymer component content of %,

(η_(RC)/η_(PP))×(W_(PP)/W_(RC)): 2.6,

MFR_(RC)/MFR_(PP): 1.0,

η_(RC)/η_(PP): 1.0, and

η_(RC): 2.1.

PP-6

Propylene type block copolymer having a melt flow rate (230° C., 2.16 kgload) of 2.7 g/10 min, an ethylene content in the copolymer component of46%, a copolymer component content of 24.4%,

(η_(RC)/η_(PP))×(W_(PP)/W_(RC)): 5.0,

MFR_(RC)/MFR_(PP): 0.6,

η_(RC)/η_(PP): 1.6, and

η_(RC): 3.0.

PP-7

Propylene type block copolymer having a melt flow rate (230° C., 2.16 kgload) of 7.61 g/10 min, an ethylene content in the copolymer componentof 31%, a copolymer component content of 40.8%,

(η_(RC)/η_(PP))×(W_(PP)/W_(RC)): 4.8,

MFR_(RC)/MFR_(PP): 0.1,

η_(RC)/η_(PP): 2.1, and

η_(RC):

a molecular weight decreasing agent

1,3-bis(t-butyl-peroxyisopropyl)benzene

R-1

Ethylene-butene copolymer rubber having an ethylene content of 78% byweight and a melt flow rate of 5.8 g/10 min.

R-2

Ethylene-butene copolymer rubber having an ethylene content of 75 % byweight and a melt flow rate of 0.7 g/10 min.

R-3

Ethylene-butene copolymer rubber having an ethylene content of 78% byweight and a melt flow rate of 1.8 g/10 min.

R-4

Ethylene-butene copolymer rubber having an ethylene content of 78% byweight and a melt flow rate of 0.4 g/10 min.

EXAMPLES 1 TO 10 Comparative Examples 1 to 8

As shown in Table-1 and Table-2 described below, a propylene type blockcopolymer (PP-1, PP-2, PP-3, PP-4, PP-5, PP-6, PP-7), a molecular weightdecreasing agent and an olefin type elastomer (R-1, R-2, R-3, R-4) wereblended to obtain a composition. Then, 100 parts by weight of the saidcomposition, 0.1 parts by weight of a phenol type antioxidant and 0.1parts by weight of calcium stearate were mixed in a high-speed stirringtype mixer (Hensel Mixer, Trade name) at a room temperature for 3minutes to obtain a composition, which was then granulated by using anextruding granulator (NVC-50 manufactured by Nakamichi Kikai) at a screwdiameter of 50 mm and a cylinder setting temperature of 200° C. toobtain a composition in a pellet form.

The said composition was molded in an injection molding machine (IS-100manufactured by Toshiba Kikai) under a clamping force of 100 t, at acylinder temperature of 230° C., at an injection speed of 30 mm/secondand a water passing temperature in a mold of 50° C. to make test pieces,which were then conditioned in a chamber at a humidity of 50% and a roomtemperature of 23° C. for 72 hours. Then, a melt flow rate, a haze testand a coefficient of linear expansion were evaluated and the resultsthereof are shown in Table-1 and Table-2.

As clear from Table-1 and Table-2, Examples 1 to 10 are superior in atransparency, a coloring property and a dimensional stabilitysimultaneously compared to Comparative Examples 1 to 8.

INDUSTORIAL APPLICABILITY

Since the resinous compositions for trimming of automobiles according tothe invention have an advantage to be superior in a transparency, acoloring property and a dimensional stability, they are useful as outermaterials for automobiles such as bumpers, fenders, mauls and mud guardsetc.

TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 blending ratio of composition PP-190 89.98 PP-2 90 89.98 PP-3 90 89.98 PP-4 90 89.98 PP-5 90 89.98molecular weight decreasing agent 0.02 0.02 0.02 0.02 0.02 R-1 10 10 1010 10 10 10 10 R-2 R-3 10 10 R-4 [η]_(RC)/[η]_(PP)) × (W_(PP)/W_(RC))2.5 2.5 1.8 1.8 1.2 1.2 1.9 1.9 2.6 2.6 [MFR]_(RC)/[MFR]_(PP) 1.1 1.10.8 0.8 2.0 2.0 0.6 0.6 1.0 1.0 [MFR]_(R)/[MFR]_(PP) 1.0 1.0 1.8 1.8 0.90.9 0.6 0.6 1.0 1.0 [η]_(RC)/[η]_(PP) 1.0 1.0 1.1 1.1 0.9 0.9 1.1 1.11.0 1.0 [η]_(R)/[η]_(PP) 1.0 1.0 0.9 0.9 1.0 1.0 1.1 1.1 1.1 1.1[η]_(RC) 1.8 1.8 2.2 2.2 1.5 1.5 1.6 1.6 2.1 2.1 evaluation results meltflow rate 6.1 18.0 3.1 10.7 7.0 23.0 7.8 24.9 1.8 9.0 haze 40 43 50 5740 45 35 40 41 48 coloring property ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ ∘ coefficient oflinear expansion 8.0 9.1 7.1 8.3 7.0 8.0 7.5 8.0 8.5 9.2

TABLE 2 Comparative Example 1 2 3 4 5 6 7 8 blending ratio ofcomposition PP-1 90 PP-4 90 PP-5 90 PP-6 90 89.98 PP-7 90 89.98 90molecular weight decreasing agent 0.02 0.02 R-1 10 10 10 10 R-2 10 10R-3 10 R-4 10 [η]_(RC)/[η]_(PP)) × (W_(PP)/W_(RC)) 5.0 5.0 2.5 4.8 4.81.3 4.8 2.6 [MFR]_(RC)/[MFR]_(PP) 0.6 0.6 1.1 0.1 0.1 0.6 0.1 1.0[MFR]_(R)/[MFR]_(PP) 1.7 1.7 1.0 0.4 0.4 0.05 0.4 1.0 [η]_(RC)/[η]_(PP)1.6 1.6 1.0 1.6 1.6 1.1 1.6 1.0 [η]_(R)/[η]_(PP) 1.0 1.0 1.6 1.3 1.3 1.91.8 1.1 [η]_(RC) 3.0 3.0 1.8 2.1 2.1 1.6 2.1 2.1 evaluation results meltflow rate 3.0 11.3 3.2 7.1 23.8 23.8 5.5 1.3 haze 90 91 70 60 63 55 7360 coloring property x x x x x x x x coefficient of linear expansion12.7 13.0 9.0 12.5 14.0 9.0 13.5 11

What is claimed is:
 1. A polyolefin resin composition comprising: (A)99˜80% by weight of a propylene block copolymer, wherein said blockcopolymer consists of a propylene homopolymer component and anethylene-propylene copolymer component, and wherein a product of anintrinsic viscosity ratio of said copolymer component to saidhomopolymer component and a weight ratio of said homopolymer componentto said copolymer component is within a range of ((η_(RC)/η_(PP))×(W_(PP) /W _(RC)))=0.2˜3.0, wherein the intrinsic viscosity of saidhomopolymer component and said copolymer component being η_(PP) andη_(RC), respectively, and a weight content (%) of said homopolymer andsaid copolymer component being W_(PP) and W_(RC), respectively, andhaving a ratio of a melt flow rate of said copolymer component(MFR_(RC)) to a melt flow rate of said homopolymer (MFR_(PP)) componentwithin a range of (MFR _(RC) /MFR _(PP))=0.3˜4.0, a ratio of theintrinsic viscosity of said copolymer component to said homopolymercomponent is within a range of η_(RC)/η_(PP)=0.7˜1.2, and wherein η_(RC)is 6.5 or less, W_(RC) is within a range of 22-70% by weight and theethylene content of said copolymer component is within the range of25-55% by weight; and (B) 1˜20% by weight of an olefin or styreneelastomer, wherein a ratio of a melt flow rate of said olefin or styreneelastomer (MFR_(R)) to that of said homopolymer component (MFR_(PP)) insaid propylene block copolymer (A) is within a range of (MFR _(R) /MFR_(PP))=0.3˜4.0, and a ratio of an intrinsic viscosity of said olefin orstyrene elastomer η_(R) to that of the homopolymer component η_(PP) insaid propylene block copolymer (A) is within a range ofη_(R)/η_(PP)=0.7˜1.2.
 2. A polyolefin resin composition according toclaim 1 wherein the olefin or styrene elastomer (B) is anethylene-butene rubber.
 3. A polyolefin resin composition according toclaim 1 wherein MFR of the propylene block copolymer is with in a rangeof 2.5 to 8.7 g/10 min.
 4. A polyolefin resin composition comprising 100parts by weight of the polyolefin resin composition according to claim 1and 0.001˜0.1 parts by weight of a molecular weight decreasing agent(C).
 5. A polyolefin resin composition comprising 100 parts by weight ofthe polyolefin resin composition according to claim 2 and 0.001˜0.1parts by weight of a molecular weight decreasing agent (C).
 6. Apolyolefin resin composition comprising 100 parts by weight of thepolyolefin resin composition according to claim 3 and 0.001˜0.1 parts byweight of a molecular weight decreasing agent (C).